While PCBs are semivolatile and commonly measured in air throughout the globe, atmospheric sources of PCBs are almost completely undefined. This project will expand the knowledge of the sources and distribution of PCBs in air through a major field study coupled with atmospheric modeling. The study is structured as four aims: Under Aim 1 we will determine the prevalence and distribution of atmospheric PCBs in an urban area. We will monitor PCBs in air at select residential areas of Chicago, Illinois and East Chicago, Indiana and compare results to Columbus Junction, Iowa. Aim 1 will involve innovative methods in sampling design, including high volume sampling from parked health clinic vans and passive sampling at homes and schools. Over 1,000 air samples will be collected and analyzed for the full suite of PCB congeners each year. The logistics of air sampling will be accomplished by cooperating with local health agencies, schools, and governments. PCB congener analysis will be supported by a fully automated analytical method for atmospheric PCB extraction, concentration, cleanup, analysis, and quality assurance. Project Aims 2-4 focus on characterizing the sources using additional field measurements coupled with mathematical modeling. Aim 2 involves characterization of PCBs released from contaminated water. A field and modeling study will examine the water of Indiana Harbor / Shipping Canal in East Chicago as an emission source of PCBs. Aim 3 concerns characterization of PCBs released from the soils of a former refinery site destined to store PCB contaminated sediments. Under Aim 4 we will evaluate mechanistic models, dispersion models, and other computational models for estimating PCB emissions from other (unknown) sources in the Chicago / East Chicago urban industrial region. Aims 2-4 include considerations of the effects of season, local meteorology, topography, re-suspension of contaminated sediment, construction activities at a contaminated site, and regional dispersion.